1. Field of the Invention
The present invention relates to a ceramic dynamic-pressure bearing and a hard disk drive using the same.
2. Description of the Related Art
Conventionally, a ball bearing has often been used as a bearing for the shaft of a motor serving as a drive unit of electric equipment. High-speed rotation of a motor has been rapidly implemented in a hard disk drive, which is a peripheral component of a computer. In this regard, in order to obtain excellent bearing performance with low rotation-speed fluctuation and reduced noise and vibration, or in order to elongate bearing service life, a dynamic-pressure bearing, which uses a fluid, such as air, as a medium, has been employed. The dynamic-pressure bearing operates in the following manner: when, for example, a spindle and a bearing member disposed so as to surround the spindle undergo relative rotation about an axis, the axis of rotation is supported by the action of fluid dynamic-pressure generated in the gap formed between the outer circumferential surface of the spindle and the inner circumferential surface of the bearing member. Further, a certain other bearing is configured such that the thrust face of a spindle or that of a bearing member is supported by action of dynamic pressure through disposition of a thrust plate.
When a dynamic-pressure bearing is in a high-speed rotation state, in which generated dynamic-pressure is sufficiently high, two members which face each other with a dynamic-pressure gap present therebetween do not come into contact with each other. However, at the time of starting or stopping, when rotational speed is low, sufficiently high dynamic pressure is not generated; thus, the two members come into contact with each other. Component members of such a dynamic-pressure bearing have generally been formed of a metal, such as stainless steel, and in some cases have been further coated with resin or a like material. However, two metallic members may involve a problem of wear or seize-up caused by mutual contact thereof at the time of starting or stopping. In order to prevent the problem, coating a metallic member with a lubricating layer, such as a resin layer, at a portion facing the dynamic-pressure gap has been proposed, resulting in a failure to yield sufficient effect. In order to attain sufficient endurance against wear and seize-up, either or both of two members, such as either or both of the spindle and the bearing member described above, which face each other with a dynamic-pressure gap present therebetween have been formed of a ceramic, such as alumina.
3. Problems to be Solved by the Invention
However, in the case of a hard disk drive which employs a dynamic-pressure bearing configured such that support in the thrust direction is effected by action of dynamic pressure through use of a thrust plate, despite use of ceramic components, a problem arises in that, when a second member and a thrust plate come into contact with each other at the time of starting or stopping, wear or linking (a phenomenon such that two members come into close contact due to vacuum created in the clearance therebetween) occurs, or an increase in starting torque disables starting of rotation. Also, such a hard disk drive has involved a problem in that vibration occurs during rotation of the dynamic-pressure bearing, with resultant unstable rotation.